The invention relates to an improved method for emergency ventilating and pressurizing an aircraft cabin in case of a depressurization of the aircraft cabin, for example due to failure of an aircraft air conditioning system and the presence of a leakage or hole in a fuselage of the aircraft. The invention further relates to an improved system for emergency ventilating and pressurizing an aircraft cabin.
In an aircraft cabin, an aircraft air conditioning system known, for example, from DE 10 2006 016 541 A1 or WO 2007/115811 A1, usually ensures a necessary air exchange and controls the cabin pressure and cabin temperature. The term aircraft cabin is to be understood here as all areas of the aircraft which are to be ventilated and pressurized during normal operation of an aircraft, such as, for example, a cockpit, a passenger cabin, crew areas, and at least selected cargo compartments. The cabin internal pressure is controlled by means of a cabin pressure control system which comprises controllable air outlet valves arranged in the area of a skin of the aircraft fuselage.
If during the flight, for example due to failure of the aircraft air conditioning system and the presence of a leakage or hole in the fuselage of the aircraft, a depressurization of the aircraft cabin occurs, the aircraft descends to a safe altitude of approximately 10,000 feet (3048 meters) and flies to the destination airport or to an airfield situated nearer. In order to supply the necessary breathable air for the passengers during this period, it is known to provide aircraft with one or more so-called emergency ram air inlets which allow ram air to be fed from the aircraft environment directly into an air distribution system of the aircraft. The air distribution within the aircraft cabin is supported by controlling the air outlet valves of the cabin pressure control system into an open position.
DE 10 2008 058 451 A1 or WO 2010/057548 A1 describes a system and a method for emergency ventilation of an aircraft cabin in the specific event of a leakage occurring in the region of an air mixer of the aircraft air conditioning system. Further, DE 10 2008 056 417 A1 or WO 2010/051920 A2 discloses a system and a method for emergency ventilation of an aircraft cabin, wherein a first and a second valve, which during normal operation of the aircraft serve as air outlet valves of the cabin pressure control system, in the event of a failure of the aircraft air conditioning system, are controlled such that air is supplied from the aircraft environment into the aircraft cabin via the first valve and discharged back into the aircraft environment via the second valve.
During descent of the aircraft to the safe altitude of approximately 10,000 feet (3048 meters), the decreasing pressure within the aircraft cabin converges to the increasing ambient pressure and, in dependence on the descent rate of the aircraft and the depressurization rate within the aircraft cabin, might become lower than the ambient pressure resulting in the build-up of a so-called negative differential pressure between the aircraft cabin pressure and the ambient pressure. To ensure the integrity of the aircraft structure, the negative differential pressure should not exceed a critical value. Therefore, a negative relief valve might be provided, which opens upon occurrence of a small negative differential pressure and hence allows air from the aircraft environment to enter the aircraft cabin providing for a pressure equalization between the aircraft environment and the aircraft cabin.
As an alternative, it is known from DE 101 45 687 A1 to open the emergency ram air inlets prior to the occurrence of a negative differential pressure and to supply ram air from the aircraft environment to the aircraft cabin. The ram air supplied to the aircraft cabin provides for a partial re-pressurization of the aircraft cabin and prevents the build-up of a negative differential pressure until finally a pressure equalization between the aircraft environment and the aircraft cabin occurs.
However, independent of whether a negative relief valve or the emergency ram air inlets are used to supply ambient air from the aircraft environment to the aircraft cabin and to thus prevent a negative differential pressure to occur or at least from exceeding a critical value, a pressure equalization between the aircraft environment and the aircraft cabin might take place before the aircraft has reached the safe altitude of approximately 10,000 feet (3048 meters). In this case, the descent rate of the aircraft to the safe altitude has to be suitably controlled such that the build-up of a negative differential pressure is prevented, usually increasing the descent time of the aircraft to the safe altitude. When the aircraft has reached the safe altitude, air is supplied to the aircraft cabin via the emergency ram air inlets with the outflow valves of the cabin pressurization system being in an open position so as to support the air distribution within the aircraft cabin. As a result, during cruising at the safe altitude, the aircraft cabin remains unpressurised.